I have to use -ephemeral-ports-range as I have to open and forward ports in my router.
With
-ephemeral-ports-range 40731:40733 -capacity 3
(3 ports for 3 clients) there is the above mentioned 400 error.
With
-ephemeral-ports-range 40731:40736 -capacity 3
(6 ports for 3 clients) all is fine.
Is this documented anywhere?